The present invention relates to an electronic transducer for measuring flexion of bodies or structures and particularly bodies or structures which are soft or elastic and which may be subject to length variations during flexion. The invention has particular utility in the measurement of flexion of joints in the human body without introducing constraints but it will be apparent that the invention has wide application and is in no way limited to this particular purpose.
In one practical embodiment of the invention transducers according to the invention are mounted in or on the fingers of a glove whereby human finger motion is converted to data streams for input to a computer. Such a glove is used in professional animation production by Puppeteers.
One prior art transducer device in the form of a Puppeteer""s glove uses fibre-optic cables that circumscribe each finger of the glove through pre-sewn channels and transmit light from Light Emitting Diodes (LED""s) at one end of the cable to photo receptors at the other end of the cable. The variation in bending of the fibre-optic cable causes a variation in the light received by the receptor and thus flexion of the fingers is able to create data streams related thereto. A number of problems are inherent in these prior art devices. For example, the fibre-optic cables required for the purpose are communication grade cables which are expensive and, although flexible, are not designed for continuous flexion and consequently they have a short life span. Other problems such as connecting power to the glove and the electronic circuit components required for implementation render the gloves cumbersome and expensive to repair.
A further prior art device is described in U.S. Pat. No. 5,090,248 entitled xe2x80x9cElectronic Transducerxe2x80x9d and comprises an extensometer in the form of two or more interposed helical coils configured to allow elastic deformation thereof and preferably mounted in an elastic dielectric material which provides a restoring force to return the conductors to their original configuration after deformation. The deformation causes a change in the capacitance between the conductors (by changing the inter-electrode gap between the respective coils) and this change is monitored to measure dimensional change over a wide dynamic range. The dimensional change is essentially elongation or when the extensometer is attached to a movable joint is a combination of elongation and deflection which cannot be separated since the change in capacitance is a measure of the changes in inter-electrode""s gap due to both elongation and deflection. Therefore this prior art transducer is not suitable for measuring angular deflections reliably or accurately as would be required, for example, in the aforementioned Puppeteer""s glove or in any other situations where accurate and reproducible data is required.
Accordingly, it is an object of this invention to provide an electronic flexion transducer that overcomes one or more of the aforementioned problems, or other problems, associated with known transducers when used for measuring or monitoring flexion.
The invention provides an electronic flexion transducer comprising two or more interposed electrical conductors forming an elongate coil, said coil being bonded on one side along its length to a flexible non-extensible support surface whereby flexion of the surface causes a change in length of the coil between said one side, which retains its original length and a side opposite to said one side, thereby causing an angular separation between said conductors with a consequent change in capacitance of the coil.